A NEW METHOD FOR DETERMINATION OF PLASTIC DEFORMATION PROPERTIES AT HIGH STRAIN RATE AND ITS MODELLING Xiangfan Fang* Institute of Automotive Lightweight Design, University Siegen, D-57076 Siegen, Germany Abstract. The determination of material properties under high speed loading is a challenge. The system ringing in a conventional servo-hydraulic tensile testing machine deteriorates the quality of force measurement, which makes a precise determination of yield locus, strain hardening and fracture strain difficult. In this work, the system ringing effect of the entire tensile testing system were analyzed. It was determined that the ringing of the system is location and geometry dependent. A new type of tensile sample has been developed. Beside of the usual major plastic deformation area, it has an additional elastic area, within which a locally restricted secondary minor plastic deformation takes place. This very small plastic deformation absorbs the elastic vibrations in this area. Therefore, the deformation forces can be measured by strain gauge without any ringing effect. The plastic deformation behavior of materials can be determined for a wide range of strain rate of 0.0001 - 1000 /s exactly. To explain the functionality and the physical background of the new sample, based on the equations for one- dimensional stress waves and theory of the stress wave attenuation due to dislocation motions, a simplified beam model with analytical formulations could be established und programmed in MATLAB. Verifications show a good prediction of sample geometry using this simplified model. 1 Introduction and state of the art During a vehicle crash event, large multi-axial plastic deformation with strain rate in the range of 10 −4 − 10 3 /s occurs. The material behavior must be exactly determined and modelled for the FE simulation, which is commonly used in the vehicle development process. In order to determine the flow curves in this strain rate range, three different measuring techniques are generally used: quasi-static testing machine with 80 mm tensile specimen for 10 −4 − 10 −2 /s; servo-hydraulic high-speed testing machine with 20-25 mm smaller specimens according to ISO 26203-2 for the range up to 10 3 /s; Split-Hopkinson-Bar (SHB) for the range > 10 3 /s with very small 5-10 mm specimens (ISO 26203-1). The experimental techniques and conditions, i.e. the measurement of force, deformation, specimen geometry and size as well as the specimen fixation, are different for the strain rate ranges and produce an apparent discontinuity in material behavior [1]. *Corresponding author: [email protected] © The Authors, published by EDP Sciences. This is an open access article distributed under the terms of the Creative Commons Attribution License 4.0 (http://creativecommons.org/licenses/by/4.0/). EPJ Web of Conferences 250, 01010 (2021) DYMAT 2021 https://doi.org/10.1051/epjconf/202125001010
A NEW METHOD FOR DETERMINATION OF PLASTIC DEFORMATION PROPERTIES AT HIGH STRAIN RATE AND ITS MODELLING
Jun 23, 2023
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